The present invention relates to a chip-in-glass fluorescent indicator panel and, more particularly, to a chip-in-glass fluorescent indicator panel in which an IC shield arranged for protecting an IC and a filament fixing portion are integrated with each other.
In the structure of a conventional chip-in-glass fluorescent indicator panel, as shown in FIGS. 5 and 6, a wiring layer 1 formed by sputtering Al or printing Ag is formed on a glass substrate 17 consisting of soda-lime glass, at least one insulating layer 7 is formed by screen printing on the wiring layer 1 to prevent a pattern-like graphite layer 2 from being short-circuited to the wiring layer 1. In the insulating layer 7, holes for electrically connecting the pattern-like graphite layer 2 to the wiring layer 1, holes for connecting bonding pads on an IC 3 to bonding pads 4 on the substrate by bonding wires 5, and holes for connecting the wiring layer 1 to terminals 6 arranged for electrically connecting the internal circuit of a glass envelope 15 to an external circuit are formed. In these holes, the holes for electrically connecting the pattern-like graphite layer 2 to the wiring layer 1 are filled with graphite 8 to electrically connect the pattern-like graphite layer 2 to the wiring layer 1. The pattern-like graphite layer 2 is formed by screen printing on the insulating layer 7. In addition, a phosphor layer 9 is formed on the pattern-like graphite layer 2 by screen printing, photolithography, or the like.
A die bonding material is coated on the insulating layer 7 by using stamp pins or the like, and the IC 3 is mounted on the die bonding material. The IC 3 is fixed by curing the die bonding material, and the bonding pads on the IC 3 are connected to the bonding pads 4 on the substrate by the bonding wires 5. An IC shield 10 for preventing hot electrons emitted from a coating layer 14 of a filament 12 from being injected in the IC 3 and preventing an erroneous operation is formed on the IC 3, and a grid 11 for controlling the hot electrons from the coating layer 14 of the filament 12 is formed above the phosphor layer 9 of the pattern-like graphite layer 2. In addition, the filament 12 having a surface coated with the ternary carbonate coating layer 14 is suspended by an anchor 13 and a filament fixing portion 16 above the phosphor layer 9, the grid 11, the IC 3, and the IC shield 10. In order to easily fix the filament 12 to the anchor 13 and the filament fixing portion 16, the coating layer 14 is pealed to expose a core line at both the ends of the filament 12. These elements are assembled together with a glass envelope 15. The resultant structure is subjected to a sealing and evacuating processes to evacuate the glass envelope 15, thereby completing a chip-in-glass fluorescent indicator panel.
In the conventional chip-in-glass fluorescent indicator panel, since the IC is present between the phosphor layer 9 and the filament fixing portion 16, the long filament 12 must be stretched between the filament fixing portion 16 and the anchor 13. For this reason, a drive voltage of the filament 12 is higher than that of a normal fluorescent indicator panel. When the filament 12 is particularly driven at a low DC voltage, e.g., an anode-grid voltage of 12V or less, an anode-grid RMS voltage on the positive side of the filament 12 is decreased, thereby resulting in an insufficient luminance.
As the filament fixing portion 16 and the anchor 13 must be arranged outside the IC shield 10, the size of the package must be increased. The IC shield 10 and the filament 12 must have a sufficient interval therebetween to prevent the IC shield 10 from being in contact with the filament 12 because this contact peals the coating layer 14 of the filament 12 to expose the core line. Therefore, the luminance is disadvantageously decreased by the long interval.